1. Field of the Invention
The present invention relates to a photosensitive device for the infrared range.
2. Description of the Prior Art
In the article entitled "Electronically Scanned C.M.T. detector array for the 8-14 micrometer band", published in the review "Electronics Letters", of the Apr. 1, 1982, vol. 18, No. 7, pages 285-287, a photosensitive device for the infrared range is known which will be described with reference to FIG. 1 accompanying the present description.
This device comprises an array of N lines and M columns of infrared detectors integrated on a semiconductor substrate. In FIG. 1, M=N=3, by way of example. The detectors D.sub.11, D.sub.21, D.sub.31 . . . , D.sub.12, D.sub.22, D.sub.32 . . . are photodiodes, integrated on cadmium, mercury and telluride (C.M.T) semiconductor substrate, each photodiode being associated with an MOS transistors T.sub.1. In FIG. 1, the anode of each photodiode is connected to groud and its cathode to MOS transistor T.sub.1. A first array of horizontal electrodes connects together the MOS transistors T.sub.1 associated with the detectors of the same line. A second array of vertical electrodes connects together the gates of the MOS transistors T.sub.1 associated with the detectors in the same column. A first shift register allows each electrode of the second array to be addressed successively. When an electrode of the second array is addressed, there is integration of the charges corresponding to the infrared radiation, received by the detectors connected to this electrode, for example detectors D.sub.11, D.sub.12 , D.sub.13 in FIG. 1. The integration and reading of the charges is provided by operational amplifiers connected as integrators, with a capacity C.sub.1, C.sub.2, C.sub.3 between their negative input and their output, and which are connected to each electrode of the first array. A multiplexer receives the outputs of the amplifiers and supplies a series reading signal S of the charges integrated in the detectors of a column. The integration of the charges of detectors D.sub.21, D.sub.22, D.sub.23 of the next column then begins.
The first MOS transistors T.sub.1 as well as the first shift register are integrated on a silicon semiconductor substrate which is interconnected with the substrate bearing the infrared detectors. The first MOS transistors T.sub.1 and the first shift register are placed in the same cryostat brought to 77K as the infra red detectors.
The problem which arises, and which the present invention resolves, is that operational amplifiers connected as integrators cannot be placed inside the cryostat. Since their consumption, and so their temperature, are high, putting them in the cryostat would raise difficulties. In addition, because of this high consumption, they are constructed as discrete components and are space consuming.
The consequence is that numerous connections must be formed between the cryostat and the rest of the device. In addition, the connections between the cryostat and the operational amplifiers convey low level signals sensitive to parasites.